New External Fixators for Treatment of Pelvis and ... · acetabulum fractures was designed and...

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Abstract— At first, the doctors mentioned their own

medical experience with treatment of complex pelvic injury in patients with polytrauma and give reasons for necessity of early stabilization of pelvic fractures by means of external fixation, especially with continuous hemorrhage into lesser pelvis region and the retroperitoneum. Afterwards they used damage control surgery methods including selective embolization. However, this article is focused also on the design of external fixators applied in traumatology and orthopaedics (i.e skills of engineers). These fixators can be used in the treatment of open and unstable (i.e. complicated) fractures of pelvis and its acetabulum. Two versions (i.e. old and new) are compared. Numerical modelling (i.e. Finite Element Method), together with CAD modelling, experiments, material engineering, and nanotechnology are presented as a support for developing of a new design of external fixators.

Keywords—traumatology, pelvis, complex injuries, polytrauma, acetabulum, fractures, design, biomechanics, numerical modeling

I. INTRODUCTION NCREASING number of high-energy injuries brings increase in number of complex injuries of the pelvis,

where apart from fractures of the pelvic girdle also arteries, nerves, soft tissues and pelvic intraperitoneal and retroperitoneal organs are injured. The most severe complication of these injuries consists in extensive hemorrhage, mainly from injured skeleton, a presacral

Assoc. Prof. M.Sc. Karel FRYDRÝŠEK, Ph.D., ING-PAED IGIP, Department of Mechanics of Materials, Faculty of Mechanical Engineering, VŠB – Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava, Czech Republic (phone: +420 597323495, e-mail: [email protected]).

Assoc. prof., M.D. Leopold PLEVA, Ph.D., Trauma Centre, University Hospital in Ostrava, 17. listopadu 1790, 708 52, Ostrava, Czech Republic (e-mail: [email protected]).

M.Sc. Jaroslav JOŘENEK; Department of Mechanics of Materials; Faculty of Mechanical Engineering, VŠB - Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava, Czech Republic (e-mail: [email protected]).

M.D. Vladimír JEČMÍNEK, Ph.D., Trauma Centre, University Hospital in Ostrava, 17. listopadu 1790, 708 52, Ostrava, Czech Republic (e-mail: [email protected]).

M.Sc. Richard KLUČKA, Department of Mechanics of Materials, Faculty of Mechanical Engineering, VŠB – Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava, Czech Republic (e-mail: [email protected]).

M.Sc. Milan SIVERA, Department of Mechanics of Materials, Faculty of Mechanical Engineering, VŠB – Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava, Czech Republic (e-mail: [email protected]).

and paravesical vascular plexes that can directly threaten life of the injured child by hemorrhagic traumatic shock.

Diagnostic methods, apart from RTG pelvic, are ultrasonography, computer tomography and computed angiotomography, see [1].

The basis for the treatment of instable pelvic fractures consists of pelvic skeleton stabilization, which in the urgent stage is ensured by application of a pelvic clamp with subsequent application of external fixator, see [1] − [4], [7] − [12] and Fig. 1.

Fig. 1 Complex pelvis fracture treated with external fixator

(Trauma Centre, University Hospital in Ostrava, Ostrava, Czech Republic)

In case of continuous hemorrhage, we perform urgent

AG with surgical treatment of injured arteries or their selective embolization, see [5]. In extensive devastating injuries we do not hesitate to perform tamponade of the pelvis with possible bilateral ligature of a. iliaca interna, see [6].

II. EXTERNAL FIXATORS However, this article reports about the designing of

external fixators applied in traumatology and orthopaedics. This work was performed by VŠB – Technical University of Ostrava together with University Hospital in Ostrava and company MEDIN a.s. (Czech Republic), see web page [9] and [10] (i.e. work of the project External Fixation, see Fig. 2 and 3).

New External Fixators for Treatment of Pelvis and Acetabulum Fractures

K. Frydrýšek, L. Pleva, J. Jořenek, V. Ječmínek, R. Klučka, M. Sivera

I

INTERNATIONAL JOURNAL OF BIOLOGY AND BIOMEDICAL ENGINEERING

Issue 2, Volume 7, 2013 36

Fig. 2 Focus of our project “External Fixation”, see web

page [9].

Fig. 3 Application of external fixator (treatment of a dog,

treatment of a human - experiments in the laboratory at VŠB – Technical university of Ostrava)

External fixation, see Fig. 2 and 3, is a surgical

treatment usually used to set bone fractures in which a cast (plaster) would not allow proper alignment of the fracture. In this kind of treatment, holes are drilled into uninjured areas of bones around the fracture and special bolts or wires are screwed into the holes. Outside the body, rods and curved pieces of metal with special joints (bracket) connect the bolts to make a stiff support. The complicated fracture, see Fig. 3 and 4, can be set in the proper anatomical configuration, see ref. [1] − [16].

Fig. 4 Application of external fixator (consequences of

poliomyelitis, foot deformities, source internet)

III. FIXATORS FOR TREATMENT OF PELVIS AND ACETABULAR FRACTURES

This article is focused on the external fixators intended for pelvis. These fixators can be applied in the treatment of open and unstable (i.e. complicated) fractures of pelvis and its acetabulum, for example see Fig. 5 and a radiograph presented in Fig. 6.

Fig. 5 Examples of pelvis fracture

Fig. 6 Fracture of pelvis and its acetabulum (anteroposterior

radiograph - transverse with posterior wall acetabular fracture)

Acetabular fractures, see Fig. 6 and 7, either occur with high-energy trauma (e.g. automobile collisions, falls, etc.) or as an insufficiency fracture. In younger patients, there is almost always significant trauma, and commonly associated injuries, when an acetabular fracture occurs. In elderly patients, acetabular fractures can occur due to bone weakened (i.e. consequences of osteoporosis, periprosthetic fractures etc.).



Fig. 7 Examples of acetabular fractures

Fig. 8 Application of external fixator for treatment of

pelvis and its acetabulum

IV. NEW REQUIREMENTS FOR DESIGNING EXTERNAL FIXATORS

At the VŠB – Technical University, two designs of external fixators intended for treatment of pelvis and acetabulum fractures was designed and tested (i.e. an old version noted as “Option 1” and a new and modern version noted as “Option 2”), see Fig. 8 and ref. [7] and [12].

DEMANDS: BENEFITS AND EXPLANATION: GOALS: Outer parts of fixators must be x-ray invisible

(i.e. low x-ray absorption):

Easy to see fracture; reducing radiation exposure for patients and surgeons; shortening the operating time.

New smart materials

(mostly not metal)

Antibacterial protection:

Application of nanoadditives containing selected metal-based nanoparticles on the surface of the outer parts of the fixators may allow for growth inhibition of several

pathogens and thus prevent or reduce possible infection. Antibacterial protection gives products an added level of protection against damaging microbes such as, bacteria, mould and mildew that can cause cross-contamination and product deterioration. Antibacterial nanotechnology, combined with regular cleaning practices, helps to

improve hygiene standards and provides extra protection wherever it is used. Antibacterial protection based on the nanotechnology was tested in the laboratory

conditions. Material Engineering: Material proposition and material tests; proper mechanical properties. Ecological perspective: Easy to recycle.

Weight optimalization: To avoid the overloading of limbs fixed by external construction. This is based on the application of numerical methods and experiments too.

New design (structure) Patient's comfort:

Reducing the time of the surgical operation and reducing the overall cost. Technical aesthetics of fixators also have impacts on the psyche of the patients (i.e. "friendly-

looking design of fixators"). For example, patients usually have better feelings, easier motion and physiotherapy with fixators made up from lighter composites (reinforced

plastics) than heavier metals. Easy to assembly:

Proper mechanical properties:

Stiffness of the whole system of fixators, fatigue testing, etc. are based on laboratory testing of new smart materials.

Numerical modelling

(FEM, SBRA Method) and experiments

Measuring of the real loadings:

During the patient’s treatment measurements of the real loadings and stiffness of the external fixators (laboratory measurement and measurement in vivo - painlessly) and data processing are needed. This is based on strain gauge measurement and applied

statistics and the Simulation-Based Reliability Assessment (SBRA) Method, see [17] − [26]. This type of measuring and processing in vivo has never been applied

before to the solution of problems of external fixators. Table I New ways for designing external fixators applied in treatment of open and unstable fractures



Scientific and technical developments, together with medical care and practice and engineering bring new demands for designs of external fixators. These demands are presented in Table I.

Two versions of external fixators (“Option 1” and “Option 2”) were solved, see Fig. 8.

V. EXPERIMENTS The “Option 1” is fully metallic (i.e. the old design which

does not satisfy the new demands presented in Table I). On the contrary, the “Option 2” is partly metallic (i.e. the

new design which satisfies the new demands presented in Table I). There are composite rods made of carbon fibres which are x-ray invisible, see Fig. 8.

The new types of external fixators for treatment of fractures of pelvis and its acetabulum were tested in the laboratory at the VŠB – Technical University of Ostrava (Ostrava, Czech Republic), see [15] and Fig. 9.

Fig. 9 Measurements in the laboratory

The experiments were focused mainly on the stiffness and

reliability for the whole system of the fixator and pelvis interaction (i.e. pulling the hip bone outwards from acetabulum after the reposition of pelvis fragments – axial tensile force 100 N in Schanz screw).

VI. NUMERICAL MODELLING The CAD models of external fixators (i.e. “Option 1” and

“Option 2”), see Fig. 8), were imported into the Finite Element (FE) software Ansys Workbench. In this software, the FE meshes were created, see Fig. 10 and 11.

Fig. 10 FE mesh for external fixator (whole structure)

Fig. 11 FE mesh for external fixator (detail)

The basic information about the boundary conditions is

presented in Fig. 12. There are defined mechanical contacts with friction between the brackets and titanium pipes (“Option 1”) or between the brackets and composite rods (“Option 2”) and between brackets and Schanz screws.

Fig. 12 FE model (boundary conditions) of external fixator for pelvis

and its acetabulum

Schanz screws are embedded in pelvis and its acetabulum in drilled holes. Their attachments are modelled by elastic supports (i.e. by Winkler's foundation, see point “A” and “B” in Fig. 12). The elastic support (defined via modulus of foundation K /Nm-3/, see Fig. 12) is applied in the radial and axial direction on the surface parts of Schanz screws. This is quite good and popular simplification of the real complicated interaction between screw and bone, see [16], [19] and



[27] − [29]. Loading force 100 N (see point “C” in Fig. 12) is explained

in the end of Chapter V. From the results, for example see Fig. 13, 14, Table II and

[16], is evident very important improvement of the new design (i.e. the new design “Option 2” is better than the design “Option 1”). In the Table II, the symbols “ ” or “ ” mean the positive or negative aspects in designing.

Fig. 13 “Option 1” - FE modelling of external fixator for pelvis and

acetabulum (equivalent stresses for tensile loading 100 N)

ATTRIBUTES: OPTION 1: OPTION 2: Design: old new

Material: titanium,

stainless steel carbon fibre,

titanium, stainless steel

Added antibacterial protection:

no yes

X-ray invisible: no partly yes Weight of

external fixator decreasing

Stiffness of external fixator: increasing

Maximum von Mises stresses

/MPa/: 97.1, see Fig. 17

85.6 – decreasing, see Fig. 18

Maximum total deformation

/mm/: 5.74 4.32 - decreasing

Patient comforts: improvement Reliability assessment improvement

Easy to assembly: the same Table II Results comparing – external fixator for pelvis and its

acetabulum (designs “Option 1” and “option 2”)

Fig. 14 “Option 2” - FE modelling of external fixator for pelvis and

acetabulum (equivalent stresses for tensile loading 100 N)

VII. CONCLUSION According to the results presented in Table II (i.e.

comparing of the new design with the old one), the improvements in the designing of external fixators for treatment of pelvis and acetabulum fractures are evident.

The results of experiments fit well with numerical modelling.

VŠB - Technical University of Ostrava together with University Hospital of Ostrava and Trauma Hospital of Brno are now in the middle of a process creating new designs for external fixators. Hence, they are in cooperation with the Czech producers MEDIN Nové Město na Moravě (Czech Republic). Therefore, all results could not be published in this paper due to confidentiality reasons.

Report about the new ways to design of external fixator for the treatment of fractures of pelvis and its acetabulum, based on the results of previous research, was presented. Hence, the new designs and materials of fixators will satisfy the ambitious demands of modern traumatology, surgery and economics.

ACKNOWLEDGMENT This work has been supported by the Czech projects MPO

FR-TI3/818 “External Fixation” and by Czech project TA03010804 “Osteosynthesis of Leg and Arm Fractures” and by Czech-Slovak project 7AMB12SK123 resp. SK-CZ-0028 “Theory and Practice of Structures on Elastic Foundations”.

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Assoc. Prof. M.Sc. Karel FRYDRÝŠEK, Ph.D., ING-PAED IGIP (Department of Mechanics of Materials, Faculty of Mechanical Engineering, VŠB – Technical University of Ostrava, Ostrava, Czech Republic) - born in June 27th 1972, married, one daughter. Study: M.Sc. - 1995, Ph.D. - 1999, Assoc. Prof. - 2009 in the branch of "Applied Mechanics" all at the Faculty of Mechanical Engineering VŠB – Technical University of Ostrava. He also studied pedagogy in the branch of "Academic Pedagogy for Teachers-Engineers According to the European Standards IGIP" at the Centre for Study of Academic Teaching in the Prague -2003. Scientific-research activities and cooperation with industry: Theory and practice of FEM and other numerical methods, strength and elasticity, plasticity, material tests, fatigue, thermal stresses, creep, comparing of experiments and calculations, stress-strain analyses in bodies, proposition of testing machines and its parts, rock mechanics, geomechanics, mechanics of composites and structures on elastic foundation. He has a rich cooperation with industry (automotive industry, railway industry, civil engineering, mining, metallurgy, forming, casting, heat technology, steel structures, pipe systems, biomechanics etc.). In the last years, he is focused on probabilistic reliability assessment (SBRA Method applications) and biomechanics (problems of design of external & internal fixators for treatment of open and unstable fractures in traumatology and orthopaedics). Assoc. prof., M.D. Leopold PLEVA, Ph.D., Head Physician, Trauma Centre, University Hospital in Ostrava, 17. listopadu 1790, 708 52, Ostrava, Czech Republic (e-mail: [email protected]). Under the leadership of Assoc. prof. Leopold Pleva, the Trauma Centre currently draws on significant traditions by introducing new operating methods in polytrauma, which are concentrated in the Trauma Center from the whole North-Moravian region. The scientific research activity focuses on solution of state research tasks, where the physicians of the Trauma Center are successful solvers of new therapeutic methods. M.Sc. Jaroslav JOŘENEK; Ph.D. student in the branch of “Applied Mechanics”, Department of Mechanics of Materials; Faculty of Mechanical Engineering, VŠB - Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava, Czech Republic (e-mail: [email protected]).



M.D. Vladimír JEČMÍNEK, Ph.D., Trauma Centre, University Hospital in Ostrava, 17. listopadu 1790, 708 52, Ostrava, Czech Republic (e-mail: [email protected]). M.Sc. Richard KLUČKA; Ph.D. student in the branch of “Applied Mechanics”, Department of Mechanics of Materials, Faculty of Mechanical Engineering, VŠB – Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava, Czech Republic (e-mail: [email protected]). M.Sc. Milan SIVERA; Ph.D. student in the branch of “Applied Mechanics”, Department of Mechanics of Materials, Faculty of Mechanical Engineering, VŠB – Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava, Czech Republic (e-mail: [email protected]).



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